Beacon protection in a wireless network

ABSTRACT

A wireless station implements a technique to reduce the occurrence of collisions between messages in a wireless network by dynamically modify a message interval during a communication session, based on received information indicative of beacon timing. The technique can be implemented by an access point on a wireless local area network to reduce collisions of beacon transmissions. The received information can include information indicative of beacon timing of other wireless stations, difficulty of a wireless station in receiving beacon transmissions, device capabilities, and/or other information.

FIELD OF THE INVENTION

At least one embodiment of the present invention pertains to wirelesscommunications, and more particularly, to avoidance of beacon collisionsin a wireless network.

BACKGROUND

The Institute of Electrical and Electronics Engineers (IEEE) standard802.11 is perhaps the most commonly implemented communications standardtoday in the context of wireless local area networks (WLANs). Variousversions of and amendments to this standard have been published to date,including 802.11a, 802.11b, 802.11g, 802.11n, 802.11-2012, 802.1ac,802.1ad, 802.1ah, etc. (collectively and individually “IEEE 802.11” orsimply “802.11”).

Under 802.11, an access point (AP) transmits various managementmessages, called “frames,” to other wireless stations. One type ofmanagement frame is called a beacon frame, or simply “beacon.” Beaconsare sent periodically by an AP to synchronize a wireless network. Abeacon contains key information about the network, including atimestamp, the beacon interval, capability Information, service setidentifier (SSID), supported rates, etc. The beacon identifies thepresence of an AP, and clients and APs can maintain timingsynchronization by using the time stamp in the beacon.

When a wireless station receives a beacon from another wireless station,its radio interface determines the received signal strength of thebeacon, along with capability information and information regarding thenetwork. In a network environment that includes multiple APs, a non-APwireless station uses a received signal strength indicator (RSSI) andcapability information to rank APs and decide which APs to attempt touse. An AP can use other APs' beacons to determine how many other APsare within communications range and which channels they use. An AP canalso take into account other APs' information to select certainparameters, such as its channel of operation.

The beacon in 802.11 also supports use of power-saving mode by low-powerclients, including battery operated devices. With infrastructurenetworks, an AP will buffer frames destined for sleeping stations andannounce which clients have frames queued for them by use of a trafficindication map (TIM).

Under current implementations of 802.11, APs generally transmit beaconsat intervals of approximately 100 ms or 200 ms. No channel reservationis done for purposes of sending beacons. Instead, 802.11 mandates use ofa Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) algorithmfor purposes of sending beacons and other messages. If another stationis sending a frame when a beacon is to be sent, then the AP shoulddetect this condition and “back off”, i.e., wait until the other stationis done transmitting. Consequently, the actual time between twoconsecutive beacons may be longer than the beacon interval. CSMA/CA doesnot always work perfectly, however, and when it does not, beacons maycollide with (i.e., temporally overlap) messages transmitted by otherstations (including beacons of other APs). Additionally, the crystaloscillator used to derive the clock in an AP typically has somefrequency drift, which can affect the timing of beacon transmissions andthereby contribute to beacon collisions with other messages.

Beacon collisions can have a significant impact on performance and powerconsumption and are therefore undesirable. When beacons from two APscollide, new clients may not be able to detect one or both of the APs.Further, clients that are already associated to an AP and are in theactive state may not be able to synchronize themselves to the AP.Additionally, a client in power saving mode may have extra delays inreceiving packets, may have to stay awake longer (e.g., to receive thebeacon), and may even become disconnected from the AP and have toreconnect. Extra activity on the client side due to beacon collisionsalso consumes excess power on the client, which can be a significantissue for battery-operated (e.g., mobile) clients.

In addition to CSMA/CA and frequency drift, there are other known causesfor beacon collisions, such as the so-called “hidden node” problem. SomeAPs may not be within wireless range of each other, yet there areclients that can detect the presence of both APs. As a result, theCSMA/CA back-off procedure employed by a given AP may not work in thissituation. Additionally, some APs may be within range of each other butstill may not detect another AP's beacon, due to fading or receiverfailure, for example. Further, some APs have poor physical layer or MACimplementations, and therefore, they may transmit beacons and otherpackets when they should not.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the present invention are illustrated by wayof example and not limitation in the figures of the accompanyingdrawings, in which like references indicate similar elements.

FIG. 1 illustrates an example of an environment in which a beaconprotection technique can be implemented.

FIG. 2 illustrates an example of a beacon frame including a modifiedbeacon interval field.

FIG. 3 illustrates an example of an information element forcommunicating a change in beacon period.

FIG. 4A is a flow diagram showing an example of a process of modifying abeacon interval.

FIG. 4B is a flow diagram showing an example of a process of setting abeacon interval immediately upon boot-up, based on other detectedbeacons.

FIG. 5 is a block diagram showing an example of a hardware architectureof a wireless station that can implement the beacon protectiontechniques described herein.

FIG. 6 illustrates a beacon protection engine that can be implemented ina wireless station.

DETAILED DESCRIPTION

In this description, references to “an embodiment”, “one embodiment” orthe like, mean that the particular feature, function, structure orcharacteristic being described is included in at least one embodiment ofthe technique introduced here. Occurrences of such phrases in thisspecification do not necessarily all refer to the same embodiment. Onthe other hand, the embodiments referred to also are not necessarilymutually exclusive.

Introduced here are techniques for reducing collisions between messagesin a wireless network, such as beacon collisions, by, for example,enabling a wireless access point to dynamically modify its beaconinterval during a communication session, based on current networkconditions. The disclosed techniques are particularly, though notexclusively, applicable to and advantageous for reducing beaconcollisions in an IEEE 802.11 compliant network. Note, however, thatwhile the disclosed techniques are described in the context of IEEE802.11 to facilitate explanation, it is not limited in applicability tobeacon messages or to IEEE 802.11 based communications. It iscontemplated that the techniques introduced here can be appliedadvantageously to other types of communication networks and protocols.Such other types of communication networks and protocols may include,for example, Ethernet, Bluetooth, Bluetooth Low Energy (BLE), IEEE802.16 (WiMax), or a cellular telecommunications standard such as 3GPPLong-Term Evolution (LTE) or LTE-Advanced (LTE-A), and various othertechnologies.

Note also that in this description, the term “IEEE 802.11” or “802.11”is intended to encompass any and all existing and/or futureamendments/versions of IEEE standard 802.11, unless otherwise stated orphysically impossible. Additionally, in this description the terms“client” and “non-AP station” are generally used interchangeably, eventhough in certain instances an AP may function as a client.

Under IEEE 802.11, a parameter called Target Beacon Transmission Time(TBTT) is the time at which a node (i.e., an AP, or a non-AP station inad-hoc mode) must send a beacon. The time difference between twoconsecutive TBTTs is known as the beacon interval. The beacon intervalis given in Time Units (TU), where each TU represents 1,024microseconds. The beacon interval is typically set to 100 TUs (102,400microseconds, or 102.4 ms) and its length is two bytes.

In a technique introduced here, an 802.11 compliant AP can decide tomodify its beacon interval during a communication session, based oninformation indicative of beacon timing that it acquires from one ormore other wireless stations. The beacon interval can be modifiedaccording to, for example, a randomization criterion or a predeterminednumerical sequence, to reduce the possibility of beacon collisions. Theacquired information upon which the AP bases its decision to modify thebeacon interval can include actual detected beacons of one or more otherAPs, information from non-AP stations indicative of other APs' beacons,or other types of information, such as client type or capabilitiesinformation, an indication that another wireless station is havingdifficulty receiving beacons, etc. When an AP modifies its beaconinterval in this manner, the new beacon interval can be communicated toassociated stations in the existing beacon interval field according tocurrent versions of 802.11, or in a modified (e.g., extended) beaconinterval field such as described below.

FIG. 1 shows an example of an environment in which the beacon protectiontechniques introduced here can be applied. The illustrated environmentincludes multiple APs 2 a, 2 b and 2 c (collectively APs 2) and multiplenon-AP stations (or “STAs”) 3, all operating in compliance with IEEE802.11. At least one of the APs 2 may be connected to a wired network 4,such as the Internet, as shown. In the illustrated environment, eachnon-AP station 3 is within a wireless communications range 5 a, 5 b or 5c of each AP 2 a, 2 b or 2 c, respectively, and therefore each non-APstation 3 can detect and receive messages from all of the illustratedAPs 3. However, none of the APs 2 is within range of, or can detect orreceive messages from, any other AP. This example therefore illustratesthe “hidden node” scenario. Dynamic modification of beacon interval canbe used in a scenario to avoid beacon collisions. For example, one ormore of the APs 2 each may receive an indication from one or more non-APstations 3 that the non-AP station is having difficulty receiving theAP's beacon, which may be interpreted as an indication of beaconcollisions. An AP 3 can then modify its own beacon interval to avoidbeacon collisions.

In a technique introduced here, different APs may choose differentbeacon intervals, such that consecutive beacons do not have same targetbeacon transmission time. The beacon interval may be chosen such that itis some predetermined number of microseconds different from the otherknown AP beacon intervals being used. Alternatively, the beacon intervalcan be randomized between specified acceptable values, or simplyrandomized within some specified range of values.

An AP can change its beacon interval over time if, for example, itreceives beacons from other APs with beacon interval close to its ownbeacon interval. Beacons alternatively can be transmitted by an AP insome other pattern, such as at different intervals over time where theinterval values follow a known or predetermined sequence of numbers. Thesequence of numbers can be communicated to non-AP stations using anexisting or modified beacon interval field such as described below.

In certain embodiments, beacons are transmitted periodically but atdifferent intervals for different APs. An AP can scan the operatingchannel to determine which beacon intervals are being used, and canavoid using any beacon interval that is less some minimum number ofmicroseconds different from the beacon intervals already being used.Additionally, an AP can delegate to non-AP stations the task of scanningthe channel and reporting back to the AP the beacon intervals that areused, as described further below to avoid hidden node issues.

It is possible to choose the beacon interval from a wide variety ofvalues. Note, however, that increasing the beacon interval may causedelay in the association and roaming process, because stations scanningfor available APs may miss the beacons. On the other hand, it may reducethe overall number of beacons and associated overhead in a given periodof time. Conversely, decreasing the beacon interval may result in thequickest association and roaming process, but there will likely beadditional overhead.

Under 802.11, a beacon frame is a type of management frame. FIG. 2illustrates the general format of a management frame 20, of which abeacon frame is one type. As shown, a management frame includes amulti-field MAC header, a frame body, and a frame check sequence (FCS).The information that is unique to each type management frame (e.g., abeacon frame) is contained within the frame body. In a beacon frame, theframe body includes a timestamp field, beacon interval field, capabilityfield, SSID field, supported rates field, etc. The beacon interval field21 may be two octets in length, for example.

As noted above, the modified beacon interval can be communicated toother stations in the standard beacon interval field as defined undercurrent versions of 802.11, or in a modified beacon interval field. Insome embodiments, the standard 802.11 beacon interval field is replacedby an extended beacon interval field 21, which includes the standardbeacon interval field 23 already available under (for example)802.11-2012 and a beacon interval extension field 24. The alreadyavailable beacon interval field 23 together with the beacon intervalextension field 24 are collectively referred to herein as the new,modified or extended beacon interval field 21. The new beacon intervalfield 21 can be used to provide backward compatibility to accommodatestations that do not have the ability to dynamically modify the beaconinterval or to receive a dynamically modified beacon interval.

Alternatively, in some embodiments the already available beacon intervalfield 23 is modified to convey the beacon transmission patterns that arenot using the same beacon interval. For example, a predetermined beaconinterval number (e.g., a very large number that is unlikely to be used)may be used to communicate a predefined beacon transmission pattern thatdoes not use the same beacon interval for all beacons. One extra octet,e.g., a mode field, for example, may be added to describe the beacontransmission pattern, as shown in FIG. 2. Additional octets may be addedto show different patterns or different periods, if necessary.

In some embodiments, an AP may decide what beacon pattern or beaconinterval to use based on the type(s) of clients that are associated tothe AP and/or the capabilities of such clients. One such criterion maybe, for example, whether a non-AP station has the capability to detectand adjust to a modified beacon interval. A non-AP station with suchcapability can notify an AP of that capability by using a probe request,association request or other management frame or control frame.

As another example, a non-AP station can notify an AP as to what levelof power requirement it has, where different levels of power requirementcan be defined, which notification may be used to tell the AP howimportant it is for the client to be able to receive beacons on time andto track beacons without issues. The AP can then use this information todecide whether to modify its beacon interval. The power requirement canbe communicated to the AP during association, or after the associationif the power requirement changes over time. If there are legacy clientsnear an AP that do not support the new beacon patterns, in order tomaintain backward compatibility the AP may use a regular interval forall clients, or it may transmit beacons in the regular interval and in amodified interval.

An AP can modify its beacon interval dynamically (i.e., during acommunication session) multiple times, if for example current networkconditions make it necessary or desirable to do so. An AP may adjust itsbeacon interval after it has booted up and has started its beacon forvarious reasons, such as if it is receiving beacons from neighboring APswith the same or very similar beacon interval as its own. Other reasonsfor dynamic adjustment of the beacon interval might include, forexample: the AP detecting multiple delays in transmitting its beacon dueto backing off to another AP's beacon; receiving a report from a clientthat there is another AP in proximity the client (or other clients) withthe same or similar value of beacon interval; or receiving a report fromone or more clients indicating that they are having difficulty receivingmultiple beacons from one or more APs.

Any of various procedures can be employed by an AP to modify its beaconinterval. In one embodiment, the AP scans for beacon timing informationand collects beacon timing information from associated clients and, insome cases, from neighboring APs. The AP then selects the best beaconinterval that is sufficiently different from the beacon intervals of anyother nearby APs. An algorithm may be employed to select the new beaconinterval, which may be based on a randomization criterion and/or apredefined numerical sequence.

Once beacon interval selection is complete, the AP communicates toassociated clients that it intends to change the beacon interval andwhen it intends to do so, by using any of various different methods. Forexample, the beacon itself can be used to indicate the time at which thebeacon interval will change. Alternatively, an action frame (e.g., asdefined in 802.11) may be used to indicate the time at which the beaconinterval will change. As another alternative the time of change ofbeacon interval may be communicated using other types of frames, such asother data, control, or management frames.

An information element may be used to communicate the time at which achange of beacon period will occur. FIG. 3 illustrates an example ofsuch an information element. The information element 30 contains anElement Identifier (ID) field, Length field, Mode field, New BeaconInterval field, and Beacon Interval (BI) Switch Count field. The NewBeacon Interval field can be set to the number interval, e.g., acountdown (in terms of the number of beacons) until the beacon intervalchanges. The Mode field specifies the new beacon interval pattern or anyother optional information that needs to be communicated. The BI SwitchCount field either is set to the number of beacons until the stationsending the BI switch announcement element switches to the new channelor is set to 0. In some embodiments, a value of 1 for BI Switch Countindicates that the switch of beacon interval occurs immediately beforethe next beacon, whereas a value of 0 indicates that the switch occursat any time after the frame containing the element is transmitted. Insome embodiments, at the request of the AP whose beacon interval isbeing modified, a non-AP station may broadcast or forward a BI switchannouncement on behalf of that AP.

FIG. 4A illustrates a process that can be employed by an AP to reducethe likelihood of beacon collisions. Initially, at step 401 the APbroadcasts beacon messages wirelessly for receipt by at least one otherwireless station, according to a first beacon interval. The otherwireless station(s) can include one or more APs and/or non-AP stations.Next, at step 402, the AP receives a second message from one of theother wireless stations (a “second wireless station”) over a wirelesslink, including information indicative (directly or indirectly) ofbeacon timing. The information in the second message may have beenrequested by the AP, or it may be received by the AP not based on anyprior request. The second wireless station may be another AP or a non-APstation. If the second wireless station is another AP, the secondmessage may be a beacon of the other AP, in which case the secondmessage is directly indicative of beacon timing; or it may be anothertype of message bearing information indicative of beacon timing. Thesecond message alternatively can be from a non-AP station and includeinformation on beacon timing (e.g., beacon interval) of another AP thatmay be out of range of the first AP. Alternatively, the second messagecan be, for example, a message from a non-AP station indicating that thenon-AP station is having difficulty detecting beacons, in which case thesecond message is only indirectly indicative of beacon timing.

At step 403, the AP then determines a new beacon interval that isdifferent from its original beacon interval (the “first beaconinterval”), based on information in the second message, and using theappropriate algorithm. As noted above, the algorithm may be based on arandomization criterion and/or a predetermined set of values. The APthen transmits, at step 404, one or more message(s) to other stations toannounce the impending change to its beacon interval. The announcementindicates what the new beacon interval will be and when it will begin.The announcement may be transmitted by broadcast, multicast or unicast,depending on client capabilities, for example. At step 405, at thedesignated time the AP begins broadcasting beacon messages, for receiptby the at least one other wireless station, according to the new beaconinterval.

In some embodiments, immediately after an AP boots up, it scans forother APs nearby and picks a beacon interval or beacon pattern that isdifferent from those of the nearby APs. FIG. 4B shows an example of aprocess that an AP may perform to do so. Initially upon power-on orreset, the AP boots up (initializes) at step 411. Next, at step 412, theAP scans for nearby APs, for example, by detecting their beacons. The APthen determines the beacon interval of each detected AP, from the beaconof each detected AP, at step 413. At step 414, the AP selects a beaconinterval that is different from the beacon interval of each detected AP.At step 415, at the designated time the AP begins broadcasting beaconmessages, for receipt by the at least one other wireless station,according to its selected beacon interval.

Various other beacon protection techniques can be employed to reducebeacon collisions, in addition to or instead of dynamically modifyingthe beacon interval. These techniques may be employed if, for example,an AP detects beacon collisions despite having selected or modified itsbeacon interval in attempt to avoid such collisions, or if it detectsany condition that is suggestive of beacon collisions or beacon delays.For example, a beacon guard time can be added immediately before beacontransmissions. In current implementations of 802.11, downlink and uplinktraffic compete with beacon transmissions, such that beacons sometimesget delayed due to downlink or uplink traffic. To ensure that there is aclear channel at a targeted beacon time, a mechanism can be employed tocause an AP and client to refrain from transmission some predeterminednumber of milliseconds before the TBTT for some or all beacons. A newinformation element can be defined, by which the AP specifies to clientsat which time interval before the beacon they shall clear the channel.The new information element can be transmitted as part of a beacon,probe request, probe response, or other management or control frame.

Additionally, to force legacy clients or clients with other basicservice set identifiers (BSSIDs) off the air prior to a beacontransmission, an AP or a client directed by an AP can attempt to reservethe medium some predetermined number of milliseconds before some or allbeacons are supposed to be transmitted. In that situation, the AP cansend a clear-to-send to self (CTS2SELF) message to clear the channel.The AP can perform a modified request send/clear to send (RTS/CTS)message exchange with a client to reserve the channel for the durationof the protected beacons.

In another approach, the CSMA/CA algorithm can be modified to provideprotection for beacons. In current implementations, the beacon istransmitted following CSMA/CA according to best efforts., i.e., with lowpriority. As a result, beacons get delayed. Therefore, in accordancewith a technique introduced here, an AP may instead use higher priorityqueues for beacons, such as used in the enhanced distributed channelaccess (EDCA) mechanism, to avoid large contention windows and decreasebeacon delays. Alternatively, an AP can define a separate set of CSMA/CAback-off parameters only for beacons, or may overrule the CSMA/CA forbeacons and transmit a beacon if it sees the channel is clear for somepredetermined number of time slots.

FIG. 5 illustrates an example of a hardware architecture of a wirelessstation, such as an AP, that can implement any of the beacon protectiontechniques described above. The illustrated wireless station 50 includesone or more main processors 51, memory 52, one or more mass storagedevices 53, a wired communication adapter 54, and an RF subsystem 55,all coupled to each other through an interconnect 56. The interconnect56 may be or include one or more conductive traces, buses,point-to-point connections, controllers, adapters and/or otherconventional connection devices. The main processor(s) 51 (which mayinclude one or more multicore processors) control the overall operationof the wireless station 50 and can be or include, for example, one ormore general-purpose programmable microprocessors, digital signalprocessors (DSPs), mobile application processors, microcontrollers,application specific integrated circuits (ASICs), programmable gatearrays (PGAs), or the like, or a combination of such devices.

Memory 52 can be or include one or more physical storage devices, whichmay be in the form of random access memory (RAM), read-only memory (ROM)(which may be erasable and programmable), flash memory, miniature harddisk drive, or other suitable type of storage device, or a combinationof such devices. The mass storage device(s) 53 can be or include one ormore hard drives, digital versatile disks (DVDs), flash memories, or thelike. Memory 52 and/or mass storage 53 can store (individually orcollectively) code 62 or 63, i.e., data and instructions, that configurethe main processor(s) 51 to execute operations to implement thetechniques described above. The wired communication adapter 54 may be orinclude, for example, an Ethernet adapter, cable modem, DSL adapter, orthe like, or a combination thereof. In certain embodiments, the wirelessstation 50 may further include one or more I/O devices (not shown), suchas a display device, audio speaker, keyboard, mouse or other pointingdevice, microphone, camera, etc.

The RF subsystem 55 includes one or more baseband processors 57 toprocess baseband signal signals, memory 58, one or more RF transceivers59. The wireless station 50 further includes one or more antennas 60coupled to the RF transceiver(s) 59. Memory 58 may store code (i.e.,instructions and/or data) 62 that, when executed by the basebandprocessors 57 and/or main processors 51, causes the wireless station 50to perform the beacon protection techniques described above. In oneembodiment, the RF subsystem 55 is or includes a Wi-Fi chip configuredto operate in compliance with IEEE 802.11. In other embodiments, the RFsubsystem 55 may instead or additionally operate according to one ormore other communication standards, such as Ethernet, Bluetooth, BLE, ora cellular telecommunications standard such as 3GPP LTE or LTE-A.

FIG. 6 illustrates a beacon protection engine that can be implemented ina wireless station, in accordance with the techniques introduced here.As shown, the beacon protection engine 65 includes a beacon timingdetermination module 66 and a beacon interval adjustment module 67. Thebeacon timing determination module 66 is responsible for, among otherthings, acquiring beacon timing information from other wireless stationsin the manner described above, and based on that information,determining if and when an adjustment to the wireless station's ownbeacon interval is appropriate. The beacon interval adjustment module 67is responsible for, among other things, selecting a new beacon intervalin the manner described above, when appropriate, and notifying otherwireless stations of the new beacon interval in the manner describedabove. In the context of the system of FIG. 5, the beacon protectionengine 65 can be implemented as the main processor(s) 51, basebandprocessor(s) 57, or another component or components within the wirelessstation 50, or its functionality may be distributed between suchcomponents. Furthermore, in various embodiments the beacon timingdetermination module 66 and beacon interval adjustment module 67 may beintegrated into a single module; similarly, the beacon protection engine65 may include additional modules that may perform other beaconprotection techniques, and may be implemented in a distributed manneramong multiple physical components. The beacon protection engine 65 canbe implemented in the form of, for example, programmable circuitry(e.g., one or more programmable microprocessors) programmed to performthe techniques described above, or as special-purpose hardwiredcircuitry, such as one or more application-specific integrated circuits(ASICs), programmable logic devices (PLDs), field-programmable gatearrays (FPGAs), etc.; or it may be implemented as a combination ofprogrammable and hardwired circuitry.

The machine-implemented operations described above can be implemented byprogrammable circuitry programmed/configured by software, or entirely byspecial-purpose circuitry, or by a combination of such forms. Suchspecial-purpose circuitry (if any) can be in the form of, for example,one or more application-specific integrated circuits (ASICs),programmable logic devices (PLDs), field-programmable gate arrays(FPGAs), system-on-a-chip systems (SOCs), etc.

Software to implement the techniques introduced here may be stored on amachine-readable storage medium and may be executed by one or moregeneral-purpose or special-purpose programmable microprocessors. A“machine-readable medium”, as the term is used herein, includes anymechanism that can store information in a form accessible by a machine(a machine may be, for example, a computer, network device, cellularphone, personal digital assistant (PDA), manufacturing tool, any devicewith one or more processors, etc.). For example, a machine-accessiblemedium includes recordable/non-recordable media (e.g., read-only memory(ROM); random access memory (RAM); magnetic disk storage media; opticalstorage media; flash memory devices; etc.), etc.

The term “logic”, as used herein, means: a) special-purpose hardwiredcircuitry, such as one or more application-specific integrated circuits(ASICs), programmable logic devices (PLDs), field programmable gatearrays (FPGAs), or other similar device(s); b) programmable circuitryprogrammed with software, such as one or more programmed general-purposemicroprocessors, digital signal processors (DSPs) and/ormicrocontrollers, system-on-a-chip systems (SOCs), or other similardevice(s); or c) a combination of the forms mentioned in a) and b).

EXAMPLES OF CERTAIN EMBODIMENTS

Certain embodiments of the technology introduced herein are summarizedin the following numbered examples:

1. A wireless station comprising: a radio frequency (RF) transceiver; anantenna coupled to the RF transceiver; and a processor coupled to the RFtransceiver and configured to cause the wireless station to transmitbeacon messages over a wireless link to at least one receiving wirelessstation during a communication session, according to a first beaconinterval; modify the beacon interval during the communication session;and transmit beacon messages over the wireless link during thecommunication session, according to the modified beacon interval.

2. A wireless station as recited in example 1, wherein the wirelessstation is an access point (AP) as defined in IEEE standard 802.11, andthe wireless link is a wireless link established in accordance with IEEEstandard 802.11.

3. A wireless station as recited in example 1 or 2, wherein theprocessor is further configured to cause the wireless station to scanwirelessly to acquire beacon timing information, prior to dynamicallymodifying the beacon interval, and wherein dynamically modifying thebeacon interval is based on beacon timing information acquired by thewireless station.

4. A wireless station as recited in any of examples 1 through 3, whereinthe processor is configured to modify the beacon interval based on acriterion designed to reduce a likelihood that beacon messages from thefirst wireless station will temporally overlap beacon messages fromanother wireless station that is within a communications range of saidat least one receiving wireless station.

5. A wireless station as recited in any of examples 1 through 4, whereinthe processor is configured to modify the beacon interval based on atleast one of: an indication of at least one other wireless stationtransmitting beacon messages in proximity to the wireless station; anindication of another beacon interval associated with beacon messagesfrom another wireless station; an indication of a type or types of otherwireless station or stations associated to the wireless station; or anindication of another wireless station having difficulty in receivingbeacon messages from multiple sources.

6. A wireless station as recited in any of examples 1 through 5, whereinthe processor is further configured to inform the at least one otherwireless station of the modified beacon interval by generating a beaconframe that includes an extended beacon interval field containing anindication of the second beacon interval, the extended beacon intervalfield including a standard beacon interval field portion and an extendedbeacon interval field portion; and transmitting, by the wirelessstation, the beacon frame including the extended interval field.

7. A wireless station as recited in any of examples 1 through 6, whereinthe processor is further configured to initiate a beacon protectiontechnique in response to a beacon collision, wherein the beaconprotection technique includes at least one of: imposing a guard intervalimmediately prior to beacon messages transmitted by the wirelessstation; or using a clear-to-send (CTS) protocol to clear a channel fortransmission of a beacon message from the wireless station.

8. A wireless access point (AP) comprising: a plurality of antennas; anda radio frequency (RF) subsystem coupled to the plurality of antennas,the RF subsystem including an RF transceiver and a processor coupled tothe RF transceiver, the processor configured to cause the wireless AP toestablish an association to at least one other wireless station over awireless link in accordance with IEEE standard 802.11, the processorfurther configured to cause the wireless AP to transmit beacon messagesin accordance with IEEE standard 802.11, for receipt by the at least oneother wireless station, according to a first beacon interval; receive asecond message over the wireless link; determine a second beaconinterval that is different from the first beacon interval, based oninformation in the second message; and transmit beacon messages inaccordance with IEEE standard 802.11, for receipt by the at least oneother wireless station, according to the second beacon interval.

9. A wireless AP as recited in example 8, wherein the processor isconfigured to determine the second beacon interval by: identifying athird beacon interval associated with beacon messages being transmittedby another wireless AP; and determining the second beacon interval basedon the third beacon interval.

10. A wireless AP as recited in example 8 or 9, wherein determining thesecond beacon interval based on the third beacon interval comprisesselecting the second beacon interval to be different from the thirdbeacon interval.

11. A wireless AP as recited in any of examples 8 through 10, whereinthe processor is configured to determine the second beacon intervalbased on a predetermined criterion designed to reduce a likelihood thatbeacon messages from the first wireless station will temporally overlapbeacon messages from another wireless station that is within acommunications range of said at least one receiving wireless station.

12. A wireless AP as recited in any of examples 8 through 11, whereinthe processor is configured to determine the second beacon intervalbased on a randomization criterion.

13. A wireless AP as recited in any of examples 8 through 12, whereinthe processor is configured to determine the second beacon interval byselecting the second beacon interval from among a plurality ofpredetermined interval values according to a randomization criterion.

14. A wireless AP as recited in any of examples 8 through 13, whereinthe processor is configured to determine the second beacon intervalaccording to a predetermined numerical sequence.

15. A wireless AP as recited in any of examples 8 through 14, whereinthe second message comprises an indication of a third beacon intervalassociated with beacon messages from a wireless station other than thefirst wireless station, and wherein the processor is configured todetermine the second beacon interval based on the indication.

16. A wireless AP as recited in any of examples 8 through 15, whereinthe second message is a beacon message from the second wireless station.

17. A wireless AP as recited in any of examples 8 through 15, whereinthe second message is not a beacon message.

18. A wireless AP as recited in any of examples 8 through 17, whereinthe information in the second message comprises an indication of apresence of at least one other wireless AP, and wherein the processor isconfigured to determine the second beacon interval based on theindication.

19. A wireless AP as recited in any of examples 8 through 18, whereinthe indication comprises an indication of a beacon interval of said atleast one other wireless AP.

20. A wireless AP as recited in any of examples 8 through 19, whereinthe information in the second message comprises an indication of a typeor types of other wireless station or stations associated to the firstwireless station, and wherein the processor is configured to determinethe second beacon interval based on the indication.

21. A wireless AP as recited in any of examples 8 through 20, whereinthe information in the second message comprises an indication of acapability of at least one other wireless station associated to thefirst wireless station, and wherein the processor is configured todetermine the second beacon interval based on the indication.

22. A wireless AP as recited in any of examples 8 through 21, whereinthe information in the second message comprises an indication of anotherwireless station having difficulty in receiving beacon messages frommultiple sources, and wherein the processor is configured to determinethe second beacon interval based on the indication.

23. A wireless AP as recited in any of examples 8 through 22, whereinthe processor is further configured to inform the at least one otherwireless station of the second beacon interval by generating a beaconframe that includes an extended beacon interval field containing anindication of the second beacon interval, the extended beacon intervalfield including a standard beacon interval field portion and an extendedbeacon interval field portion; and transmitting, by the wirelessstation, the beacon frame including the extended interval field.

24. A wireless AP as recited in any of examples 8 through 23, whereinthe processor is further configured to cause the wireless AP to transmita message to a second wireless station to request that the secondwireless station scan for beacon messages from other wireless stations.

25. A method comprising: transmitting, by a first wireless station,beacon messages wirelessly for receipt by at least one other wirelessstation, according to a first beacon interval; receiving, by the firstwireless station, a second message from a second wireless station over awireless link; determining, by the first wireless station, a secondbeacon interval that is different from the first beacon interval, basedon information in the second message; and transmitting, by the firstwireless station, beacon messages for receipt by the at least one otherwireless station, according to the second beacon interval.

26. A method as recited in example 25, wherein the processor isconfigured to determine the second beacon interval by: identifying athird beacon interval associated with beacon messages being transmittedby another wireless station; and selecting the second beacon interval tobe different from the third beacon interval.

27. A method as recited in example 25 or 26, wherein said determiningthe second beacon interval is based on a predetermined criteriondesigned to reduce a likelihood that beacon messages from the firstwireless station will temporally overlap beacon messages from anotherwireless station that is within a communications range of said at leastone receiving wireless station.

28. A method as recited in any of examples 25 through 27, wherein thesecond message comprises an indication of a third beacon intervalassociated with beacon messages from a wireless station other than thefirst wireless station, and wherein said determining the second beaconinterval is based on the indication.

29. A method as recited in any of examples 25 through 28, wherein thesecond message is a beacon message from the second wireless station.

30. A method as recited in any of examples 25 through 28, wherein thesecond message is not a beacon message.

31. A method as recited in any of examples 25 through 30, wherein thefirst wireless station is a wireless access point (AP), the secondwireless station is a non-AP wireless station, the information in thesecond message comprises an indication of a presence of at least oneother wireless AP, and wherein said determining the second beaconinterval is based on the indication.

32. A method as recited in any of examples 25 through 31, wherein theindication comprises an indication of a beacon interval of said at leastone other wireless AP.

33. A method as recited in any of examples 25 through 32, wherein theinformation in the second message comprises at least one of: anindication of a type or types of other wireless station or stationsassociated to the first wireless station; an indication of a capabilityof at least one other wireless station associated to the first wirelessstation; or an indication of another wireless station having difficultyin receiving beacon messages from multiple sources; and wherein saiddetermining the second beacon interval is based on the indication

34. A method as recited in any of examples 25 through 33, furthercomprising informing the at least one other wireless station of thesecond beacon interval by generating a beacon frame that includes anextended beacon interval field containing an indication of the secondbeacon interval, the extended beacon interval field including a standardbeacon interval field portion and an extended beacon interval fieldportion; and transmitting, by the wireless station, the beacon frameincluding the extended interval field.

35. A method of operating a first wireless station, the methodcomprising: in response to an initialization of the first wirelessstation, scanning a signal environment of the first wireless station todetect one or more other wireless stations that transmit beaconmessages, determining a beacon interval of beacon messages transmittedby each of the one or more other wireless stations that transmit beaconmessages, and selecting a beacon interval for beacon messages to betransmitted from the first wireless station, based on a result of saiddetermining; and transmitting beacon messages from the first wirelessstation according to the selected beacon interval.

36. A method as recited in example 35, wherein selecting the beaconinterval for beacon messages to be transmitted from the first wirelessstation comprises selecting the beacon interval to be different from thebeacon interval of each of the one or more other wireless stations.

37. A first wireless station comprising: means for transmitting beaconmessages wirelessly for receipt by at least one other wireless station,according to a first beacon interval; means for receiving a secondmessage from a second wireless station over a wireless link; means fordetermining a second beacon interval that is different from the firstbeacon interval, based on information in the second message; and meansfor transmitting beacon messages for receipt by the at least one otherwireless station, according to the second beacon interval.

38. A first wireless station as recited in example 37, wherein theprocessor is configured to determine the second beacon interval by:identifying a third beacon interval associated with beacon messagesbeing transmitted by another wireless station; and selecting the secondbeacon interval to be different from the third beacon interval.

39. A first wireless station as recited in example 37 or 38, whereinsaid determining the second beacon interval is based on a predeterminedcriterion designed to reduce a likelihood that beacon messages from thefirst wireless station will temporally overlap beacon messages fromanother wireless station that is within a communications range of saidat least one receiving wireless station.

40. A first wireless station as recited in any of examples 37 through39, wherein the second message comprises an indication of a third beaconinterval associated with beacon messages from a wireless station otherthan the first wireless station, and wherein said determining the secondbeacon interval is based on the indication.

41. A first wireless station as recited in any of examples 37 through40, wherein the second message is a beacon message from the secondwireless station.

42. A first wireless station as recited in any of examples 37 through40, wherein the second message is not a beacon message.

43. A first wireless station as recited in any of examples 37 through42, wherein the first wireless station is a wireless access point (AP),the second wireless station is a non-AP wireless station, theinformation in the second message comprises an indication of a presenceof at least one other wireless AP, and wherein said determining thesecond beacon interval is based on the indication.

44. A first wireless station as recited in any of examples 37 through43, wherein the indication comprises an indication of a beacon intervalof said at least one other wireless AP.

45. A first wireless station as recited in any of examples 37 through44, wherein the information in the second message comprises at least oneof: an indication of a type or types of other wireless station orstations associated to the first wireless station; an indication of acapability of at least one other wireless station associated to thefirst wireless station; or an indication of another wireless stationhaving difficulty in receiving beacon messages from multiple sources;and wherein said determining the second beacon interval is based on theindication

46. A first wireless station as recited in any of examples 37 through45, further comprising informing the at least one other wireless stationof the second beacon interval by generating a beacon frame that includesan extended beacon interval field containing an indication of the secondbeacon interval, the extended beacon interval field including a standardbeacon interval field portion and an extended beacon interval fieldportion; and transmitting, by the wireless station, the beacon frameincluding the extended interval field.

47. A first wireless station, the method comprising: means forresponding to an initialization of the first wireless station byscanning a signal environment of the first wireless station to detectone or more other wireless stations that transmit beacon messages,determining a beacon interval of beacon messages transmitted by each ofthe one or more other wireless stations that transmit beacon messages,and selecting a beacon interval for beacon messages to be transmittedfrom the first wireless station, based on a result of said determining;and means for transmitting beacon messages from the first wirelessstation according to the selected beacon interval.

48. A first wireless station as recited in example 47, wherein selectingthe beacon interval for beacon messages to be transmitted from the firstwireless station comprises selecting the beacon interval to be differentfrom the beacon interval of each of the one or more other wirelessstations.

Any or all of the features and functions described above can be combinedwith each other, except to the extent it may be otherwise stated aboveor to the extent that any such embodiments may be incompatible by virtueof their function or structure, as will be apparent to persons ofordinary skill in the art. Unless contrary to physical possibility, itis envisioned that (i) the methods/steps described herein may beperformed in any sequence and/or in any combination, and that (ii) thecomponents of respective embodiments may be combined in any manner.

Although the subject matter has been described in language specific tostructural features and/or acts, it is to be understood that the subjectmatter defined in the appended claims is not necessarily limited to thespecific features or acts described above. Rather, the specific featuresand acts described above are disclosed as examples of implementing theclaims and other equivalent features and acts are intended to be withinthe scope of the claims.

What is claimed is:
 1. A first wireless station comprising: a radiofrequency (RF) transceiver; an antenna coupled to the RF transceiver;and a processor coupled to the RF transceiver and configured to causethe first wireless station to: transmit beacon messages over a wirelesslink to at least one receiving wireless station during a communicationsession, according to a beacon interval; modify the beacon intervalduring the communication session by selecting a new beacon interval fromamong a plurality of predetermined interval values according to arandomization criterion; transmit beacon messages over the wireless linkduring the communication session, according to the new beacon interval;and perform at least one of: apply a particular one or more carriersense multiple access with collision detection (CSMA/CD) back-offparameters only to beacon messages, for purposes of transmitting beaconmessages from the first wireless station; or overrule CSMA/CD forpurposes of transmitting beacon messages from the first wirelessstation.
 2. A first wireless station as recited in claim 1, wherein thefirst wireless station is an access point (AP) as defined in IEEEstandard 802.11, and the wireless link is a wireless link established inaccordance with IEEE standard 802.11.
 3. A first wireless station asrecited in claim 1, wherein the processor is further configured to causethe first wireless station to scan wirelessly to acquire beacon timinginformation, prior to dynamically modifying the beacon interval, andwherein dynamically modifying the beacon interval is based on beacontiming information acquired by the first wireless station.
 4. A firstwireless station as recited in claim 1, wherein the processor isconfigured to modify the beacon interval based on a criterion designedto reduce a likelihood that beacon messages from the first wirelessstation will temporally overlap beacon messages from another receivingwireless station that is within a communications range of said at leastone receiving wireless station.
 5. A first wireless station as recitedin claim 4, wherein the processor is configured to modify the beaconinterval based on at least one of: an indication of at least onereceiving wireless station transmitting beacon messages in proximity tothe first wireless station; an indication of another beacon intervalassociated with beacon messages from another receiving wireless station;an indication of a type or types of receiving wireless station orstations associated to the first wireless station; or an indication ofanother receiving wireless station having difficulty in receiving beaconmessages from multiple sources.
 6. A first wireless station as recitedin claim 1, wherein the processor is further configured to inform the atleast one receiving wireless station of the new beacon interval by:generating a beacon frame that includes an extended beacon intervalfield containing an indication of the second beacon interval, theextended beacon interval field including a standard beacon intervalfield portion and an extended beacon interval field portion; andtransmitting, by the first wireless station, the beacon frame includingthe extended interval field.
 7. A wireless station as recited in claim1, wherein the beacon protection technique further includes: using aclear-to-send (CTS) protocol to clear a channel for transmission of abeacon message from the first wireless station.
 8. A first wirelessstation as recited in claim 7, wherein using a clear-to-send (CTS)protocol to clear a channel for transmission of a beacon message fromthe first wireless station comprises the first wireless stationtransmitting a clear to send to self (CTS2SELF) message to clear thechannel.
 9. A first wireless station as recited in claim 1, wherein theprocessor is configured to initiate a beacon protection technique inresponse to a beacon collision, wherein the beacon protection techniqueincludes imposing a guard interval immediately prior to beacon messagestransmitted by the first wireless station.
 10. A wireless access point(AP) comprising: a plurality of antennas; and a radio frequency (RF)subsystem coupled to the plurality of antennas, the RF subsystemincluding an RF transceiver and a processor coupled to the RFtransceiver, the processor configured to cause the wireless AP toestablish an association to at least one receiving wireless station overa wireless link in accordance with IEEE standard 802.11, the processorfurther configured to cause the wireless AP to: transmit beacon messagesin accordance with IEEE standard 802.11, for receipt by the at least onereceiving wireless station, according to a first beacon interval, thebeacon messages including a first message; receive a second message overthe wireless link; determine a second beacon interval that is differentfrom the first beacon interval, based on information in the secondmessage, by selecting the second beacon interval from among a pluralityof predetermined interval values according to a randomization criterion;transmit beacon messages in accordance with IEEE standard 802.11, forreceipt by the at least one receiving wireless station, according to thesecond beacon interval; and perform at least one of: apply a particularone or more carrier sense multiple access with collision detection(CSMA/CD) back-off parameters only to beacon messages, for purposes oftransmitting beacon messages from the first wireless station; oroverrule CSMA/CD for purposes of transmitting beacon messages from thefirst wireless station.
 11. A wireless AP as recited in claim 10,wherein the processor is configured to determine the second beaconinterval by: identifying a third beacon interval associated with beaconmessages being transmitted by another wireless AP; and determining thesecond beacon interval based on the third beacon interval.
 12. Awireless AP as recited in claim 11, wherein determining the secondbeacon interval based on the third beacon interval comprises selectingthe second beacon interval to be different from the third beaconinterval.
 13. A wireless AP as recited in claim 10, wherein theprocessor is configured to determine the second beacon interval based ona predetermined criterion designed to reduce a likelihood that beaconmessages from the wireless AP will temporally overlap beacon messagesfrom another receiving wireless station that is within a communicationsrange of said at least one receiving wireless station.
 14. A wireless APas recited in claim 10, wherein the processor is configured to determinethe second beacon interval according to a predetermined numericalsequence.
 15. A wireless AP as recited in claim 10, wherein the secondmessage comprises an indication of a third beacon interval associatedwith beacon messages from a wireless station other than the wireless AP,and wherein the processor is configured to determine the second beaconinterval based on the indication.
 16. A wireless AP as recited in claim15, wherein the second message is a beacon message from said wirelessstation other than the wireless AP.
 17. A wireless AP as recited inclaim 15, wherein the second message is not a beacon message.
 18. Awireless AP as recited in claim 10, wherein the information in thesecond message comprises an indication of a presence of at least onereceiving wireless AP, and wherein the processor is configured todetermine the second beacon interval based on the indication.
 19. Awireless AP as recited in claim 18, wherein the indication comprises anindication of a beacon interval of said at least one receiving wirelessAP.
 20. A wireless AP as recited in claim 10, wherein the information inthe second message comprises an indication of a type or types ofreceiving wireless station or stations associated to the wireless AP,and wherein the processor is configured to determine the second beaconinterval based on the indication.
 21. A wireless AP as recited in claim10, wherein the information in the second message comprises anindication of a capability of at least one receiving wireless stationassociated to the wireless AP, and wherein the processor is configuredto determine the second beacon interval based on the indication.
 22. Awireless AP as recited in claim 10, wherein the processor is furtherconfigured to inform the at least one receiving wireless station of thesecond beacon interval by: generating a beacon frame that includes anextended beacon interval field containing an indication of the secondbeacon interval, the extended beacon interval field including a standardbeacon interval field portion and an extended beacon interval fieldportion; and transmitting, by the wireless station, the beacon frameincluding the extended interval field.
 23. A wireless AP as recited inclaim 10, wherein the processor is further configured to cause thewireless AP to transmit a message to a second wireless station torequest that the second wireless station scan for beacon messages fromother receiving wireless stations.
 24. A wireless AP as recited in claim10, wherein the processor is configured to initiate a beacon protectiontechnique in response to a beacon collision, wherein the beaconprotection technique includes imposing a guard interval immediatelyprior to beacon messages transmitted by the wireless AP.
 25. A methodcomprising: transmitting, by a first wireless station, beacon messageswirelessly for receipt by at least one receiving wireless station,according to a first beacon interval, the beacon messages including afirst message; receiving, by the first wireless station, a secondmessage from a second wireless station over a wireless link;determining, by the first wireless station, a second beacon intervalthat is different from the first beacon interval, based on informationin the second message, by selecting the second beacon interval fromamong a plurality of different predetermined interval values accordingto a randomization criterion; transmitting, by the first wirelessstation, beacon messages for receipt by the at least one receivingwireless station, according to the second beacon interval; andperforming at least one of: applying a particular one or more carriersense multiple access with collision detection (CSMA/CD) back-offparameters only to beacon messages, for purposes of transmitting beaconmessages from the first wireless station; or overruling CSMA/CD forpurposes of transmitting beacon messages from the first wirelessstation.
 26. A method as recited in claim 25, wherein the processor isconfigured to determine the second beacon interval by: identifying athird beacon interval associated with beacon messages being transmittedby another wireless station; and selecting the second beacon interval tobe different from the third beacon interval.
 27. A method as recited inclaim 25, wherein said determining the second beacon interval is basedon a predetermined criterion designed to reduce a likelihood that beaconmessages from the first wireless station will temporally overlap beaconmessages from another wireless station that is within a communicationsrange of said at least one receiving wireless station.
 28. A method asrecited in claim 25, wherein the second message comprises an indicationof a third beacon interval associated with beacon messages from awireless station other than the first wireless station, and wherein saiddetermining the second beacon interval is based on the indication.
 29. Amethod as recited in claim 28, wherein the second message is a beaconmessage from the second wireless station.
 30. A method as recited inclaim 28, wherein the second message is not a beacon message.
 31. Amethod as recited in claim 25, wherein the first wireless station is awireless access point (AP), the second wireless station is a non-APwireless station, the information in the second message comprises anindication of a presence of at least one receiving wireless AP, andwherein said determining the second beacon interval is based on theindication.
 32. A method as recited in claim 31, wherein the indicationcomprises an indication of a beacon interval of said at least onereceiving wireless AP.
 33. A method as recited in claim 25, wherein theinformation in the second message comprises at least one of: anindication of a type or types of other receiving wireless station orstations associated to the first wireless station; an indication of acapability of at least one receiving wireless station associated to thefirst wireless station; or an indication of another receiving wirelessstation having difficulty in receiving beacon messages from multiplesources; and wherein said determining the second beacon interval isbased on the indication.
 34. A method as recited in claim 25, furthercomprising informing the at least one receiving wireless station of thesecond beacon interval by: generating a beacon frame that includes anextended beacon interval field containing an indication of the secondbeacon interval, the extended beacon interval field including a standardbeacon interval field portion and an extended beacon interval fieldportion; and transmitting, by the first wireless station, the beaconframe including the extended interval field.
 35. A method as recited inclaim 25, further comprising: initiating a beacon protection techniquein response to a beacon collision, wherein the beacon protectiontechnique includes imposing a guard interval immediately prior to beaconmessages transmitted by the first wireless station.